The present invention relates to a liquid overbased mixed metal stabilizer composition of calcium, barium and zinc (Ca/Ba/Zn) for stabilizing halogen-containing polymers. Shelf stable haze free liquids of overbased calcium carboxylates are used to provide a mixed metal ternary stabilizer of calcium, barium and zinc. The liquid overbased ternary system of Ca/Ba/Zn provides polymers such as polyvinyl chloride (PVC) with improvements in thermal stability, early color, plate-out resistance and clarity.
The preparation of overbased calcium or barium salts of carboxylic acids, alkyl phenols, and sulfonic acids are disclosed in the following U.S. Pat. Nos. 2,616,904; 2,760,970; 2,767,164; 2,798,852; 2,802,816; 3,027,325; 3,031,284; 3,342,733; 3,533,975; 3,773,664; and 3,779,922. The use of these overbased metal salts in the halogen-containing organic polymer is described in the following U.S. Pat. Nos. 4,159,973; 4,252,698; and 3,194,823. The use of overbased barium salt in stabilizer formulations has increased during recent years. This is due, in the main, to the fact that overbased barium salts possess performance advantages over the neutral barium salts. The performance advantages associated with overbased barium salts are low plate-out, excellent color hold, good long-term heat stability performance, good compatibility with the stabilizer components, etc. Unfortunately, most of the overbased barium salts are dark in color and, while these dark colored overbased barium salts are effective stabilizers for halogen-containing organic polymer, their dark color results in the discoloration of the end product. This feature essentially prohibits the use of dark colored overbased barium salts in applications where a light colored polymer product is desired.
According to the teachings of U.S. Pat. No. 4,665,117, light colored alkali or alkaline earth metal salts are prepared where alkyl phenol is used as a promoter. However, alkyl phenol is also a major cause for the development of color in the final product. This problem is overcome by the use of propylene oxide which displaces the hydrogen of the phenolic hydroxyl group and thereby restricts the formation of colored species. However, there are disadvantages associated with this approach, principally due to the toxic nature of propylene oxide. Propylene oxide is classified as a possible carcinogen and laboratory animal inhalation studies have shown evidence of a link to cancer. Propylene oxide is also listed as a severe eye irritant, and prolonged exposure to propylene oxide vapors may result in permanent damage to the eye. Furthermore, propylene oxide is extremely flammable and explosive in nature under certain conditions. Propylene oxide boils at 94xc2x0 F. and flashes at xe2x88x9220xc2x0 F. As a result, extreme precautions are required to handle propylene oxide at the plant site. Special storage equipment is required for propylene oxide and other safety features are necessary. U.S. Pat. No. 4,665,117 describes the use of propylene oxide at 150xc2x0 C. At this temperature, propylene oxide will be in the gaseous phase. Under these operating conditions, more than stoichiometric amounts of propylene oxide are required to carry the reaction to completion because propylene oxide will escape from the reaction mixture and this requires additional handling of the excess propylene oxide.
With the movement in the plastics industry to remove heavy metals, liquid calcium-zinc stabilizers are desirous, but not practical, as replacements for barium-cadmium or barium-zinc. Low metal concentrations, poor compatibility, haziness in clear products and plate out during processing in PVC have severely limited the universal acceptance of calcium based liquid stabilizer compositions. Problems are encountered in the stability of these compositions upon standing or storage. Storage stability is due to the incompatibility among the metal salts employed in the composition and is exhibited by increased turbidity, viscosity, or insoluble solids over time. As a result, the liquid calcium compositions are no longer homogeneous or readily pourable and must be specially treated in order to be used. U.S. Pat. No. 5,322,872 is directed to stabilized compositions of mixed metal carboxylates having improved storage stability. According to this patent, a complexing agent is added to the mixed metal carboxylate in order to improve shelf stability. Complexing agents disclosed in this patent include phosphines, phosphites, aromatic cyanides, aromatic hydroxy compounds, oximes and other compounds. U.S. Pat. Nos. 5,830,935 and 5,859,267 have also issued as directed to processes for improving basic metal salts and stabilizing halogen-containing polymers therewith.
Notwithstanding the state of the art as exemplified by the above patents, there is a need for further improvements in making compositions of overbased alkaline earth metal carboxylates and in methods for their use in stabilizing halogen-containing polymers.
The present invention relates to liquid overbased mixed metal stabilizer compositions of calcium, barium and zinc (Ca/Ba/Zn) for a halogen-containing polymer. The invention described in application Ser. No. 09/861,393, filed May 18, 2001, relates to a shelf stable haze free liquid of an overbased alkaline earth metal carboxylate. The shelf stable liquids that were described in that application have now been found to provide a mixed metal stabilizer composition with barium and zinc having improved properties in the stabilization of halogen-containing polymers.
A number of benefits are obtained by the liquid overbased Ca/Ba/Zn stabilizer products of this invention. In particular, shelf stabilities are achieved with the overbased Ca/Ba/Zn liquids with the reduction of phenol and phenolic derivatives such as phenolic reaction products. This is an especially desirable advantage in view of the efforts of the trade to reduce or eliminate such phenolic products because of environmental concerns. In addition, enhanced shelf stabilities for the liquid overbased calcium fatty acid carboxylates and barium/zinc mixed metal stabilizer compositions of this invention have been demonstrated over presently commercially available products. In particular, presently available liquid mixed metal systems exhibit the development of turbidity or haze, whereas the liquid compositions of this invention remain stable over extended periods of time. Therefore, the shelf stable and preferably haze free liquids of this invention allow easy handling, storage and filtration. Furthermore, when the liquid overbased Ca/Ba/Zn ternary stabilizer systems are employed in vinyl halide polymers, they exhibit better compatibilities with improvements in thermal stability, early color, clarity and plate-out resistance.
The Ca/Ba/Zn ternary stabilizer systems are employed in polyvinyl chloride (PVC) compositions in amounts of from about 1 to about 5 parts of stabilizer, preferably about 2-3 parts, per 100 parts PVC.
The metal ratio of Ca/Ba/Zn in such systems is on the order of about 3:14:2, within a general range of about 0.5% to 3% Ca, about 4% to 8% Ba, and about 0.5% to 3% Zn to achieve the benefits of this invention.
The above advantages, benefits and further understanding of this invention will be apparent with reference to the following detailed description and preferred embodiments.
A. Shelf Stable Haze Free Liquids of Overbased Calcium Salts for Use In the Ca/Ba/Zn System
In one preferred form of the invention, a shelf stable haze free liquid of a calcium salt of a fatty acid is used to make the Ca/Ba/Zn ternary system. The liquid comprises
a calcium carbonate,
a calcium carboxylate of a fatty acid,
a liquid hydrocarbon, and
an aliphatic alcohol having at least 8 carbon atoms, with the liquid being preferably free of a phenol or a phenolic derivative such as a phenolic reaction product.
In another form of the invention, the calcium sulfate, sulfide or sulfite may be formed instead of the carbonate where the acidic gas used in the process is sulfur dioxide, sulfur trioxide, carbon disulfide, or hydrogen sulfide.
The fatty acid of the overbased liquid calcium carboxylate is generally a C12-C22 fatty acid, including, for example, lauric, myristic, palmitic, stearic, archidic and behenic, among the saturated fatty acids. Unsaturated fatty acids include palmitoleic, oleic, linoleic, and linolenic. Among these fatty acids, oleic is presently preferred in preparing the overbased liquid carboxylates. For example, shelf stable haze free overbased calcium oleates have been prepared. These overbased calcium salts contain calcium carbonate, calcium oleate, a liquid hydrocarbon diluent and an aliphatic alcohol having at least 8 carbon atoms.
In a broad form of the invention, it is important to have an aliphatic alcohol having at least 8 carbon atoms, more preferably an alcohol having 8 to 14 carbon atoms, such as, isodecanol, dodecanol, octanol, tridecanol and tetradecanol. Isodecanol is presently preferred. It has been found that when a higher aliphatic alcohol is employed in making the overbased product, phenol may be excluded from the reaction as a promoter. This is a particularly advantageous feature of the invention where it is undesirable to have a phenol or phenolic reaction product involved in the manufacture or use of the overbased liquid.
In another form of the invention, the liquid overbased calcium salt of the fatty acid is believed to be a thermodynamically stable microemulsion. The microemulsion has micells and a continuous phase. The micells consist of an alkaline earth metal carbonate and an alkaline earth metal carboxylate of the fatty acid. The continuous phase of the microemulsion consists of the liquid hydrocarbon and the higher aliphatic alcohol.
Haze free liquids of the calcium and even barium may be employed in the Ca/Ba/Zn system. For instance, calcium or barium salts have been prepared containing at least 4% by weight or more of the alkaline earth metal up to about 36% by weight. In the case of the overbased calcium salts, up to about 13-15% by weight calcium are produced and, for barium salts, up to about 36% by weight barium may be produced. In the preparation of higher overbased products, for example, containing about 13-15% by weight metal, it has been found suitable to use a glycol or a glycol ether along with the higher aliphatic alcohol. A glycol or glycol ether may be selected from the group consisting of diethylene glycol monobutyl ether (butyl Carbitol(copyright)), triethylene glycol, dipropylene glycol, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether, and mixtures thereof.
B. The Basic Process for Making the Overbased Calcium Salts and Critical Features
The process for preparing a shelf stable haze free liquid of a calcium salt of a fatty acid comprises reacting an alkaline earth metal base and a fatty acid with an equivalent ratio of metal base to the fatty acid being greater than 1:1 in the presence of a mixture of liquid hydrocarbon. The basic process has been described in detail in application Ser. No. 09/861,393, filed May 18, 2001, of which this application is a continuation-in-part, which is incorporated in its entirety herein by reference. A surfactant and catalyst promote the reaction. The mixture is acidified and preferably carbonated to produce amorphous alkaline earth metal carbonate. During carbonation, a dispersion is added containing alkaline earth metal base, liquid hydrocarbon and an aliphatic alcohol having at least 8 carbon atoms in relative amounts at a controlled rate of base addition to produce a stable haze free liquid reaction product. Water is removed from the reaction product to produce a shelf stable haze free liquid overbased alkaline earth metal salt. Generally, it is preferred that the entire process be conducted in the absence of free oxygen and, for this purpose, an atmosphere of nitrogen is used.
One of the important features of the method is the step of adding during carbonation a dispersion of alkaline earth metal base, liquid hydrocarbon and an aliphatic alcohol having at least 8 carbon atoms at a controlled rate of base addition to produce the stable haze free liquid. It has been found that the addition of a dispersion of the base in the liquid hydrocarbon and aliphatic alcohol protects or passivates the base, thereby enabling the formation of a stable haze free liquid reaction product. By protecting or passivating the base, carbonation proceeds to produce amorphous alkaline earth metal carbonate. Unexpectedly, the reaction proceeds without the need to remove water during the reaction and results in a very stable haze free liquid reaction product. At the end of the reaction, water is removed, preferably to the level of less than 1%, more preferably less than 0.3% or 0.1%, in the obtainment of the shelf stable liquid overbased salt. The removal of water which is added during the reaction or formed by the reaction is necessitated because it forms a separate phase which impedes either the product of the reaction or the formation of a shelf stable haze free liquid.
Other features of the method include filtering the product of the reaction to produce a shelf or thermodynamically stable liquid at a product filtration rate of at least about 300 ml per 10 minutes. In a preferred form of the invention, the product which is produced is filterable to remove unwanted byproducts and enhance the shelf stability of the overbased liquid. For example, with a Buchner funnel having a 15 cm diameter under vacuum of about 25-30 inches Hg with a Whatman No. 1 filter and a diatomaceous filtering aid (Celite(copyright) 512-577), the product is filterable at satisfactory rates. One of the important discoveries of the method of this invention is the ability to filter the reaction product to form a stable haze free liquid at filtration rates which heretofore were unachievable. This was especially the case when higher levels of metal content in the overbased liquids were desired, especially overbased calcium liquids. Thus, filtration removes undesirable impurities including silica, iron oxide and other metal species, unreacted calcium hydroxide, calcium carbonate, and other oxides which may contribute to lack of stability. These byproducts or impurities may comprise up to about 6% of byproduct of the reaction.
Throughout this specification and claims, the term xe2x80x9cbasicxe2x80x9d or xe2x80x9coverbasedxe2x80x9d as applied to the alkaline earth metal salts is used to refer to metal compositions wherein the ratio of total metal contained therein to the fatty acid moieties is greater than the stoichiometric ratio of the neutral metal salt. That is, the number of metal equivalents is greater than the number of equivalents of the fatty acid. In some instances, the degree to which excess metal is found in the basic metal salt is described in terms of a xe2x80x9cmetal ratioxe2x80x9d. Metal ratio as used herein indicates the ratio of total alkaline earth metal in the oil-soluble composition to the number of equivalents of the fatty acid or organic moiety. The basic metal salts often have been referred to in the art as xe2x80x9coverbasedxe2x80x9d or xe2x80x9csuperbasedxe2x80x9d to indicate the presence of an excess of the basic component.
The above process may be used to prepare shelf stable liquids of the calcium carboxylates of the fatty acids without the use of phenol promoter or phenolic reaction product. Therefore, liquid overbased barium fatty acid carboxylates may be made for use in the ternary system of Ca/Ba/Zn without the need for a phenol or phenolic reaction product in order to achieve a shelf stable haze free liquid. In the case of liquid overbased calcium fatty acid carboxylates, shelf stable haze free products are obtained without a phenol where the aliphatic alcohol having at least 8 carbon atoms is employed.
The alkaline earth metal bases utilized as a reaction component may be derived from any calcium bases. The metal bases include metal oxides and hydroxides and, in some instances, the sulfides, hydro sulfides, etc. While a phenolic component or reactant may preferably be excluded from a reaction, in the case of liquid overbased calcium products, the phenol or alkyl phenol may be included to yield liquid overbased products. As stated above, the fatty acids, or mixtures thereof, as identified above may be used in the reaction mixture. For example, a surfactant that facilitates the reaction is the alkaline earth metal carboxylate of the fatty acid that is formed in situ. Other surfactants may be included, for example, general purpose surface active agents identified under the trademark Tween which are polyoxyethylene derivatives of fatty acid partial esters of sorbitol anhydrides, particularly mono- and di-oleates of the ethoxylated sorbitol, and polyisobutylene succinic acid. Furthermore, it is desirable to include a catalyst to facilitate the speed of the reaction such as propionic acid, citric acid, acetic acid and adipic acid. The hydrocarbon liquid employed in the process and the liquid reaction products generally includes any hydrocarbon diluent. Most generally, the liquid hydrocarbon is selected from the group of an oil, mineral spirits and non-aromatic hydrocarbons.
C. Amounts of Reactants and Catalysts
The amount of alkaline earth metal base utilized in the preparation of basic salts is an amount which is more than one equivalent of the base per equivalent of fatty acid or organic moiety, and more generally, will be an amount sufficient to provide at least three equivalents of the metal base per equivalent of the acid. Larger amounts can be utilized to form more basic compounds, and the amount of metal base included may be any amount up to that amount which is no longer effective to increase the proportion of metal in the product. When preparing the mixture, the amount of fatty acid and the alcohol included in the mixture is not critical except that the ratio of equivalents of the metal base of the combination of the other components in the mixture should be greater than 1:1 in order to provide a basic product. More generally, the ratio of equivalents will be at least 3:1. In those instances where phenol may be present in making an overbased calcium, the ratio of equivalents of monocarboxylic acid to phenol should be at least about 1.1:1; that is, the monocarboxylic acid is present in excess with respect to the phenol.
The ranges of hydrocarbon oil, aliphatic alcohol (preferably isodecanol), butyl Carbitol and triethylene glycol have been selected such that, in the presence of the alkaline earth fatty acid salt (i.e., Ca oleate) which acts as a primary surfactant, the mixture forms a stable inverse microemulsion of the metal carbonate, water, and surfactant (internal phase) and surfactant, cosurfactant, and hydrocarbon (external continuous phase).
The acceptable ratios of hydrocarbon oil to cosurfactant aliphatic alcohol (isodecanol) are about 2:1 to about 4:1, with about 2:1 preferred. The glycol ethers may be used at about 1-15% of the final product, butyl Carbitol preferably at about 6%, and triethylene glycol at about 0-2%, preferably at about 0.6%.
The lime slurry which is added to the oleic acid in the reaction is formulated to be an easily pumpable mixture with the general composition of about 40-50% lime, about 25-40% hydrocarbon oil, about 10-25% isodecanol, and about 0-10% butyl Carbitol. The butyl Carbitol amount that is needed to make a pumpable slurry increases as the % lime in the slurry increases.
The reaction mixture for an overbased calcium oleate, after addition of the slurry and carbonation with carbon dioxide, preferably has the following composition ranges:
The catalyst, propionic acid or a lower aliphatic mono, di, or tricarboxylic acid is used in the amount of about 0-0.1% of the final reaction mixture.
The step of carbonation involves treating the mixtures described above with an acidic gas in the absence of free oxygen until the titratable basicity is determined using phenolphthalein. Generally, the titratable basicity is reduced to a base number below about 10. The mixing and carbonation steps of the present invention require no unusual operating conditions other than preferably the exclusion of free oxygen. The base, fatty acid and liquid hydrocarbon are mixed, generally heated, and then treated with carbon dioxide as the acidic gas, and the mixture may be heated to a temperature which is sufficient to drive off some of the water contained in the mixture. The treatment of the mixture with the carbon dioxide preferably is conducted at elevated temperatures, and the range of temperatures used for this step may be any temperature above ambient temperature up to about 200xc2x0 C., and more preferably from a temperature of about 75xc2x0 C. to about 200xc2x0 C. Higher temperatures may be used such as 250xc2x0 C., but there is no apparent advantage in the use of such higher temperatures. Ordinarily, a temperature of about 80xc2x0 C. to 150xc2x0 C. is satisfactory.
By the term xe2x80x9cacidic gasxe2x80x9d as used in this specification and in the claims is meant a gas which upon reaction with water will produce an acid. Thus, such gases as sulfur dioxide, sulfur trioxide, carbon dioxide, carbon disulfide, hydrogen sulfide, etc., are exemplary of the acidic gases which are useful in the process of this invention. Of these acids, sulfur dioxide and carbon dioxide are preferred, and the most preferred is carbon dioxide. When carbon dioxide is used the alkaline earth carbonate is formed. When the sulfur gases are used, the sulfate, sulfide and sulfite salts are formed.
D. Halogen-Containing Polymer
A halogen-containing polymer, such as a vinyl halide resin, most commonly stabilized with the basic metal salts of this invention is polyvinyl chloride. It is to be understood, however, that this invention is not limited to a particular vinyl halide resin such as polyvinyl chloride or its copolymers. Other halogen-containing resins which are employed and which illustrate the principles of this invention include chlorinated polyethylene, chlorosulfonated polyethylene, chlorinated polyvinyl chloride, and other vinyl halide resin types. Vinyl halide resin, as understood herein, and as appreciated in the art, is a common term and is adopted to define those resins or polymers usually derived by polymerization or copolymerization of vinyl monomers including vinyl chloride with or without other comonomers such as ethylene, propylene, vinyl acetate, vinyl ethers, vinylidene chloride, methacrylate, acrylates, styrene, etc. A simple case is the conversion of vinyl chloride H2Cxe2x95x90CHCl to polyvinyl chloride (CH2CHClxe2x80x94)n wherein the halogen is bonded to the carbon atoms of the carbon chain of the polymer. Other examples of such vinyl halide resins would include vinylidene chloride polymers, vinyl chloride-vinyl ester copolymers, vinyl chloride-vinyl ether copolymers, vinyl chloride-vinylidene copolymers, vinyl chloride-propylene copolymers, chlorinated polyethylene, and the like. Of course, the vinyl halide commonly used in the industry is the chloride, although others such as bromide and fluoride may be used. Examples of the latter polymers include polyvinyl bromide, polyvinyl fluoride, and copolymers thereof.
The barium and zinc compound stabilizers which may be used with the overbased calcium salt in the ternary Ca/Ba/Zn system are well known. These metal compounds serve to capture HCl liberated during heat processing of the vinyl halide resin composition into its final shape. The barium or zinc compound stabilizers are usually metal salts of a carboxylic acid, advantageously of a C8-C24 carbon chain link monocarboxylic acid such as lauric, oleic, stearic, octoic, or similar fatty acid salts. Metal salts of alkyl phenates may be used. Mixed metal salts of carboxylic acids, and their preparation, are familiar to those skilled in the art to which this present invention pertains. Mixed metallic carboxylates involving barium/zinc blends alone and in combination with other stabilizers or additives such as beta-diketones, phosphite salts and phenolic antioxidants may be used.
E. End Uses for the Stabilizers
The overbased liquid stabilizers Ca/Ba/Zn of this invention may be used in a number of end products. Examples include:
wall covering, flooring (vinyl tile and inlay), medical devices, dip coating, chair mat, banner film, pigment dispersion, vinyl siding, piping, fuel additive, cosmetic, ceiling tile, roofing film, wear layer, play balls or toys, teethers, fencing, corrugated wall panels, dashboards, and shifter boots.
The following Examples illustrate the preparation of the shelf stable haze free liquids of the overbased calcium salts in accordance with the method of the present invention and the liquid overbased Ca/Ba/Zn stabilizers prepared therefrom. However, these examples are not considered to be limiting the scope of this invention. Unless otherwise indicated in the following examples and elsewhere in the specification and claims, all parts and percentages are by weight, and all temperatures are in degrees Fahrenheit.